The present invention relates to a tracer control method and, more particularly, to a tracer control method whereby a tracer machining inhibit area is set and tracer machining is performed while skipping the inhibit area.
A tracer appartus operates by calculating velocity commands along various axes by means of a tracer arithmetic circuit using a deflection value sensed by a tracer head, driving motors for the corresponding axes on the basis of the velocity commands along these axes to transport a tool relative to a workpiece, and repeating these operations to machine the workpiece into a shape identical to that of the model. In tracer control of this kind, the tracer head generally is made to trace the entire surface of the model to provide a machined object having a shape which is exactly the same as that of the model. There is now a requirement for tracer machining control whereby a portion of the model is skipped and both sides (or only one side) with respect to the skipped portion are traced. Such tracer machining control is well-suited for application to the machining of, say, a propeller having a boss and blades formed around the boss. The reason is that cutting solely the complicatedly shaped blade portions of a propeller under tracer control and applying NC control to cut the boss portion, which is difficult to trace because of its steep gradient, makes it possible to shorten machining time and improve the precision to which the boss portion is machined in comparison with tracer machining being applied to the entirety of the propeller.
In the prior art, if the portion desired to be skipped has, say, a concave configuration, the concave portion is flattened by being filled with clay or the like, the entire surface of the flattened model is traced to provide a machined object, and a concavity is subsequently formed in a predetermined portion of the machined object by NC control to provide the final article. With this method, however, fabricating the model is a troublesome operation. Moreover, since the skipped portion is machined to a flat shape by tracer control and is then machined into a concavity by NC control, forming the concave portion requires two operations, thereby lengthening machining time.